John Sayers' Design Forum

John Sayers' Recording Studio Design Forum

A World of Experience
Click Here for Information on John's Services
It is currently Thu Sep 24, 2020 8:58 am

All times are UTC + 10 hours




Post new topic Reply to topic  [ 7 posts ] 
Author Message
PostPosted: Fri Dec 06, 2013 9:33 am 
Offline

Joined: Wed Jun 18, 2003 5:46 pm
Posts: 5
Location: Maple Ridge, BC, Canada
hi all. i am about to begin work on retrofitting a detached garage on my property into a studio. We have had the space looked at by an engineer who has given the structure the ok - with
some reinforcement - to turn into the studio.

The first stage is to reinforce the existing structure, insulate and then begin building the inner, decoupled wall and ceiling.

some context: We are in a fairly rural area in the Pacific Northwest (fairly wet and rainy area - not too much snow falls (some years next to none) and not too hot/cold relative to the prairies etc). The garage is a 3 bay garage and is set back from the house and road and neighbours - but there are acreages around us on 3 sides for sale and there will likely be some construction happening over the next year or so around us (all on 1 acre lots). I work in recording full time and have been for the past 12 years. I do about 80% producing/engineer albums from start through completion (sometimes mastering) and about 20% mixing albums that I did not record. I need to be able to keep working throughout the inevitable home constructions around me but they won't be as close as they might in the city. This is not a mega budget, 6 month project. We will be attempting to do the bulk of the work over the next 8 weeks and trying to keep material costs to about $20k. There should be about 4 of us working on it 5 days a week. 2 skilled carpenters/builders and 2 laborers.

phase one: addressing the exterior walls and ceiling:

The outer walls are shiplap on 2x4 construction wrapped in vinyl. The vaulted ceiling is 2x4 rafters with a tin roof with collar ties. The garage doors are coming out and being framed in with 2x4 contruction.

We are going to tie in 2x6s to the ceiling rafters and lower the collar ties so that the weight is more evenly distributed. The building is wrapped with vinyl siding and we hope to replace
that with tyvek wrap and hardy board in the spring/summer.

I had been advised to add mass to the exterior walls by mounting drywall between the studs and caulking the seams. Unfortunately my builder has indicated that this poses a serious
moisture problem and is not up to code. So, we plan to insulate these exterior walls with either batt insulation or spray foam insulation. (I know this doesn't address isolation but does address R value)

Then we'll build a separate staggered stud wall with a 1 inch airspace between it and the exterior wall. (2x4 studs staggered on a 2x6 plate). We will run the insulation (not sure what type yet) between the studs.

I am reading through Rod Gervais' book and i know that different combinations of drywall layers on different faces of walls don't necessarily amount to the desired maximum STL in an intuitive way. But I haven't read of a scenario exactly like mine so I am looking for input as to get the max STL with these walls. I am hoping that the exterior wall can be addressed in some way to help with isolation so that this will function well as a double wall system.

My question is this: To get the best isolation - how much drywall should be applied and to which faces of the walls?

We are planning on adding 2 layers of 5/8ths drywall to the interior, decoupled wall on the side facing the inside of the room but should we also drywall the interior face of the exterior wall (single or double layer?) or is it better to only drywall both sides of the staggered stud wall (double layer on both?).

I am sure there will be lots of questions along the way but this is the most pressing first issue to address.

thanks!

Jon


Report this post
Top
 Profile  
 
PostPosted: Sun Dec 08, 2013 7:01 am 
Offline

Joined: Wed Jun 18, 2003 5:46 pm
Posts: 5
Location: Maple Ridge, BC, Canada
a bit of further info upon re-reading Rod's stuff and a lot more reading on the forum here.

I want to create a 2 leaf/MAM system for isolation and I am hoping that the exterior wall can function as the first layer of mass.

Although it seems like placing drywall between the existing studs on the exterior wall is a bad idea for moisture/mold reasons - we do plan to
remove the exterior vinyl and wrap with tyvek (against the shiplap) and then hardy board the exterior.

so from outdoor to indoors the construction looks like this:

Hardy Board > Tyvek wrap > shiplap > 2x4 wall with batt insulation and covered in poly for vapor barrier > 1 inch air space > staggered 2x4 wall on a 2x6 plate (w/interwoven insulation) > 2 layers of 5/8ths type X drywall.

I would expect that we need at least 50 STC to keep future construction noise OUT of the studio and to keep loud drums and amp noise IN the studio. To be honest, I am not entirely sure how to
best calculate the STC that I require as the current requirement is much less than the future will be.

What kind of STC can I hope to achieve with a wall like this?

What could/should I do additionally to achieve more STC? a third interior layer of drywall? Would it be better to add the 3rd leaf (a layer or 2 of 5/8ths directly onto the 2x4 exterior wall, after the
insulation is poly'd in)?

I understand that 3 leaf systems are less ideal than 2 - BUT if my exterior wall doesn't have enough mass to achieve decent levels of STC then should I do it?


Report this post
Top
 Profile  
 
PostPosted: Tue Dec 10, 2013 12:59 pm 
Offline
Senior Member
User avatar

Joined: Thu Aug 21, 2008 10:17 am
Posts: 11938
Location: Santiago, Chile
Hi Jon, and welcome! :)

Quote:
I had been advised to add mass to the exterior walls by mounting drywall between the studs and caulking the seams. Unfortunately my builder has indicated that this poses a serious moisture problem and is not up to code. So, we plan to insulate these exterior walls with either batt insulation or spray foam insulation. (I know this doesn't address isolation but does address R value)
You will definitely need more mass on the outer leaf, if all you have out there is Tyvek, shiplap, and siding. Is there any chance you could take that off, put thick OSB or plywood on there, then replace the Tyvek and siding on top of that? That would give you a much better base for your outer leaf, as well as improving the structural integrity of the wall (in sheer, at least). If you could double-up on the OSB (two layers, instead of the usual one) and/or replace the siding with fiber cement board, that would get you pretty much where you need to go in terms of mass on the outer leaf (unless you need extreme acoustic isolation?), and obviate the need for that "beefing up between the studs".

On the batts vs. spray foam issue: forget the spray foam. Most spray insulation is closed-cell, which is useless acoustically (some are open-cell, and might be useful, but are expensive). Your best bet is plain old fiberglass or mineral wool insulation, either as batts or as continuous roll, whatever code allows and whatever is normal for your area. But stay away from sprayed stuff, in general.

Quote:
Then we'll build a separate staggered stud wall with a 1 inch airspace between it and the exterior wall. (2x4 studs staggered on a 2x6 plate). We will run the insulation (not sure what type yet) between the studs.
You don't need a staggered stud wall there! Just plain old 2x4 framing, for each of your rooms. The goal is to have two leaves, and only two leaves (never one, never three) between any pair of adjacent rooms, or between any room and the outside world. So your outer leaf is the building shell itself (hopefully those two layers of OSB plus Hardy board!), and the inner leaf for each room will be a simple 2x4 frame with one or more layers of 5/8" drywall on only ONE side of the framing.

Quote:
I am reading through Rod Gervais' book and i know that different combinations of drywall layers on different faces of walls don't necessarily amount to the desired maximum STL in an intuitive way.
Very true! Sometimes what "seems" right and "obviously" good, in reality is not. For example, if you really did do a staggered-stud frame with drywall on both sides, that would be a 3-leaf wall, and your low frequency isolation would be pretty lousy. So your new neighbors hammering, sawing, drilling, and vehicles would make it through fairly easily. Just by taking OFF that extra layer of drywall in the middle, you INCREASE the low frequency isolation. Not intuitive at all, but very true. Rod knows what he is talking about, for sure.

Quote:
But I haven't read of a scenario exactly like mine so I am looking for input as to get the max STL with these walls. I am hoping that the exterior wall can be addressed in some way to help with isolation so that this will function well as a double wall system.
That's why I suggested taking off your existing siding / Tyvek, so all you have your studs exposed. Then put at least one and hopefully two layers of 5/8 OSB on those, followed by your Tyvek again, then either the Hardy board you mentioned (which is basically fiber cement board), or second choice some other type of siding. That gives you good mass on your outer leaf. If low frequency is a big concern for you, you could even add Green Glue between the two layers of OSB. Despite the name, it is not actually glue. It is acoustic constrained layer damping, that helps a lot with low frequency isolation. However, it is not cheap, so that might be off the cards.

If you want to get an idea of how different types of wall construction behave for acoustic isolation, then the very best document I know of for that is called "IR-761", and it's right here: http://archive.nrc-cnrc.gc.ca/obj/irc/d ... /ir761.pdf The price is right too: Free! :)

That shows literally hundreds of different methods for building walls, and the amount of acoustic isolation you can expect from each method. All of them were tested in an acoustic laboratory, and all the details are right there, with graphs and full descriptions of the materials, how they were layered, dimensions, and results. It is the "all you ever wanted to know about acoustic isolation of walls but were afraid to ask" document. Happy reading! :)

Quote:
My question is this: To get the best isolation - how much drywall should be applied and to which faces of the walls?
The answer is another question: "How much isolation do you need (in decibels)?". That's the starting point. A few simple tests with a basic sound level meter will answer that question for you, then based on the answer we can help you figure out how many layers of what you need where.

Quote:
We are planning on adding 2 layers of 5/8ths drywall to the interior, decoupled wall on the side facing the inside of the room but should we also drywall the interior face of the exterior wall (single or double layer?) or is it better to only drywall both sides of the staggered stud wall (double layer on both?).
Each frame has drywall on only ONE side o the studs, never on both sides. Each room is built as single 2x4 frame, totally disconnected from all other frames, not even touching anything, not even a single nail. Each room stands all by itself, and touches only the concrete slab, which is common to all the rooms. There are absolutely no points of contact between the framing of the individual rooms, or between the exiting structure and the framing of the rooms.

So each room has its own 2x4 frame, then you put drywall on just one side of that frame. There can be many layers of drywall (usually only two, but there might be more is special cases), but all of those layers go on the SAME side of the studs, and the other side is bare. You can put the drywall on the side that faces the room ("conventional construction") or you can put it on the other side, away from the room ("inside-out construction") which has some acoustic advantages. With inside-out construction, the studs face the room and the drywall faces the cavity: That sounds ugly and strange, but can be very useful in studios, for reasons that I'll go into later, if you think this might be something you want to do.

Quote:
I am sure there will be lots of questions along the way but this is the most pressing first issue to address.
You came to the right place for questions! That's what this place is for... :)

Quote:
I want to create a 2 leaf/MAM system for isolation and I am hoping that the exterior wall can function as the first layer of mass.
Right! It can, if done as I outlined above.

Quote:
Hardy Board > Tyvek wrap > shiplap > 2x4 wall with batt insulation and covered in poly for vapor barrier > 1 inch air space > staggered 2x4 wall on a 2x6 plate (w/interwoven insulation) > 2 layers of 5/8ths type X drywall.
If you want to keep the shilap, that's fine, but do make sure to seal all of those gaps very carefully. You also have your vapor barrier in the wrong place: it should go on the warmest side of the cavity (to prevent condensation).

What I would do is this:

Hardy Board > Tyvek wrap > 5/8" OSB > 5/8" OSB > shiplap > 2x4 wall with batt insulation > 1 inch gap (at least) > 2x4 framing on a 2x4 plate with batt insulation > 6 mil vapor barrier > 2 layers of 5/8ths type X drywall.

You might be able to skip one of the layers of OSB if the shiplap can be fully sealed, but that's a huge and time consuming job, and will cost a fortune in caulk, so it might be just as easy to slap on the second layer of OSB.

Note that the "1 inch air space" you mentioned is not really an air gap: it's just a gap between the two frames. Technically, the "air space" in an MAM wall (also know as MSM) is the total distance across the cavity between the facing surfaces of the two leaves, regardless of any insulation that might be in there. OK, so it's an issue of terminology, but you'd be surprised how important it is to get terminology right in acoustics! :) A 1 inch gap between frames means that you have an 8 inch air space... that's quite a big difference!

Quote:
I would expect that we need at least 50 STC to keep future construction noise OUT of the studio and to keep loud drums and amp noise IN the studio. To be honest, I am not entirely sure how to best calculate the STC that I require as the current requirement is much less than the future will be.
Forget STC. It is not designed for measuring studio isolation, but rather for measuring isolation of typical house / office / shop / school noises, which is mostly speech, ordinary appliances, and office equipment, at low levels. STC does not consider the bottom two and a half octaves of the musical scale at all! It is quite possible to have a wall rated at STC-60 that does a really lousy job of isolating a studio, while another wall rated at STC-45 does an outstanding job of isolating the same studio. STC is not your friend, for measuring studio isolation. What you want to be looking at is "Transmission Loss" ("TL"), which is usually expressed as dBA or dBC, and is best understood when shown on a graph, such as IR-761 does for each wall type. The pink lines on those graphs show what the STC rating would be, and you can clearly, clearly see that STC tells you nothing useful about how the wall performs in low frequency isolation.

So, to answer your question: The loudest instrument you'll be tracking is probably drums. a drum kit played normally to hard can easily hit 110-115 dB, and a dedicated drummer can do much better than that! :) A full rock band with a bunch of deaf musicians can be heading for 120 dB territory: that's entirely possibly.

So, the question is, with 120 frying your ears on the inside, how low do you need to make that on the outside? That is governed by two things, basically: 1) The law. 2) Your family and neighbors. The law specifies how loud you can be at different times of day, and for different zones. An industrial zone can be a lot louder than a residential zone, even at night. So first thing you need to do is to get a copy of your local noise regulations, probably downloadable from your municipality web site, or obtainable from their offices. Normally those regulations specify how quite your noise must be at the property line, and measured in dBA, which is good for you on both counts. dBA is less sensitive to low frequencies that dBC, and measuring at the property line means that you have plenty of feet for the sound to decay naturally after it leaves the outer surface of your wall, until it reaches the property line. Sound decays at a rate of about 6 dB each time you double the distance, so if you measured 66 dB right outside your wall at 3 feet (standard measuring distance), then that should be down to 60 dB at 6 feet, 54 dB at 12 feet, 48 dB at 24 feet, 42 dB at 48 feet, etc. So hopefully you have a lot of feet between your walls and the property line. However, that is "perfect" decay, and in reality it isn't that good: there are always things that reflect, amplify, diffuse, scatter, direct, focus, etc. the sound waves on their journey, so don't count on a true 6 db per distance doubling reduction! Probably more like 3 to 4 dB, in real life.

OK, so work backwards from your closest property line, and from the noise regulations for your area, and that will give you the MAXIMUM target level that you want outside your walls. That has you legally covered. sort of...

But then there's the "family and neighbors" factor. Your own family not agree that the noise regulations are good enough, and might want better isolation. Especially, for example, if you have babies or small children in the house that need to sleep soundly, or older kids who need quite to study. Or a wife who just likes peace and quite in her home....

And most noise regulations also have a nasty little rider in there that goes something like : "... or any other objectionable or annoying sound." Without defining what "objectionable" or "annoying" mean. Sound level meters tell you how many decibels of sound pressure are present. It doesn't tell you how many units of "objectionable" or "annoying" are present. So the cops or municipal inspectors can still shut you down and fine you, even if you are meeting the numbers, just because someone says that the remaining noise is "annoying".

In other words, it is best of you can get your level at your property line down so low that it is inaudible. That's around 30 dBA in most places.

Hopefully that will give you enough information that you can figure out how much isolation you need: Work backwards from the property line or the WAF line, until you get to your wall, and figure out what the level has to be 3 feet from your wall to not disturb anyone. Subtract that number from "how loud things will be inside", and the difference is "how much isolation you need". (The WAF line is a highly technical term in acoustics, and is defined as the precise point at which the Wife Acceptance Factor reaches exactly 100%... :)

:shot:


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.


Report this post
Top
 Profile  
 
PostPosted: Fri Dec 13, 2013 5:48 am 
Offline

Joined: Wed Jun 18, 2003 5:46 pm
Posts: 5
Location: Maple Ridge, BC, Canada
Thanks for all the info Stuart. I will try to process that and apply it as best I can.

Here's a separate question -

We are planning on ordering 4 laminated windows to have 2 windows looking out from
the MAIN ROOM (combination tracking/mixing space approx 700 sq feet) to the exterior
of the building (forest).

I have a friend doing a lot of the work on the project and he gets good rates on windows
and is passing the savings on to me. A lot window manufacturing companies are based
out here so we'll be going with pre-made windows for all the exterior.

I have a hard time translating window glass thicknesses and construction into relative
mass - do these sound sufficient to come close to the wall thickness of approx 63 STC?

These are 4x4 in size and have 6mm laminated glass > 3/8 air gap (argon filled) > 4 mm glass and one in each wall.

There would be 2 for each view to the outside - 1 on the inner 2x6 wall and 1 on the outer 2x4 wall.

thanks!


Report this post
Top
 Profile  
 
PostPosted: Fri Dec 13, 2013 7:57 am 
Offline
Senior Member
User avatar

Joined: Thu Aug 21, 2008 10:17 am
Posts: 11938
Location: Santiago, Chile
Quote:
These are 4x4 in size and have 6mm laminated glass > 3/8 air gap (argon filled) > 4 mm glass and one in each wall.
Those are typical "double glazed" window units (known as "Thermopanel" where I live), and unfortunately they are not suitable for studio isolation. Yes, you DO need two panes of laminated glass, but they need to be much thicker, and the gap between them needs to be much greater. Units like that with very thin air gaps (only 3/8"!) have very high resonant frequencies, so they do not isolate down in the low end of the spectrum, where you need it most. They are fine for typical houses, schools, offices and shops, where low frequency isolation is not needed, but they are not much use for studios.

The thickness of the glass you need depends on the surface density of the wall that it goes in. You need to keep the surface density the same or even higher for the glass as it is for the rest of the leaf. So for example, if your inner-leaf has two layers of 16mm drywall, then that would be about 24 kg/m2 surface density, so you'd need the same or greater in your glass. Since glass has a density of about 2500 kg/m3, you'd need glass at least 10mm thick for that wall, and 12mm would be a better bet. That would be made up from two layers of 6mm glass plus the acoustic interlayer between them.

And since the air gap between your leaves also needs to be consistent for the entire wall, you need the same distance between the glass panes as for the rest of the wall, or greater. So if you had a typical two-leaf wall with 8" (20cm) of air gap, then you'd need at least 20cm between the two panes, and hopefully more (to compensate for the lack of insulation in the gap).

A typical studio wall for good isolation has a pane of 12mm laminated glass in one leaf, and the second pane of 16mm or even 18mm laminated glass in the other leaf, with an air gap of 25 cm or so between them.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.


Report this post
Top
 Profile  
 
PostPosted: Fri Dec 13, 2013 11:38 am 
Offline

Joined: Wed Jun 18, 2003 5:46 pm
Posts: 5
Location: Maple Ridge, BC, Canada
thanks for the response stuart.

I am doing a little digging around to see if I can source anything like this but am starting to sense that
windows with panes as thick as you are describing are going to be very difficult to source locally
(and quite possibly way just too expensive for my budget).

Do you know of any commercially available products like what you are describing?

Do people most often build their own? I had thought for external windows that we'd need something commercially
made and sealed to keep out the elements (lots of rain here) and to be openable when circumstances permit
(mixing etc..).

An alternate idea that we are discussing is building some some large dense panels that we can mount to the walls to cover
the windows for the drum days - when the need to minimize the loudest noise is most critical.

For the other 80% of the project the source noises as so much quiter and I will have booths for amps so that may be a
way to get the benefit of natural light for 80% of the time.

Another idea that I am curious about is glass blocks. Do they provide a lot more isolation?

Thanks for all your insights and help!


Report this post
Top
 Profile  
 
PostPosted: Fri Jan 03, 2014 4:58 am 
Offline
Senior Member
User avatar

Joined: Thu Aug 21, 2008 10:17 am
Posts: 11938
Location: Santiago, Chile
Quote:
Do you know of any commercially available products like what you are describing?
There shouldn't be a problem in ordering in laminated glass: most glaziers will either stock it directly, or be able to get it for you on special order. Call around to your local suppliers to see what they have. If you can't get laminated, then ordinary thick glass will do, just not quite as well.

Quote:
Do people most often build their own?
Right. Any carpenter worth his salt can do this for you: it's just an ordinary wood, metal of vinyl window frame with thick laminated glass in it, instead of typical window glass.

Quote:
I had thought for external windows that we'd need something commercially made and sealed to keep out the elements (lots of rain here)
You can probably get a suitable unglazed frame from your local Home Depot (or equivalent) store, or if not then a good carpenter or glazier can make it for you.

Quote:
and to be openable when circumstances permit
That would be a problem! You can't open it: it should be fixed. Operable windows introduce a whole bunch of issues that I'm sure you don't wont to have to deal with, mostly related to the seals. If the window is not perfectly sealed to the frame, and the frame perfectly sealed to the wall, then you don't have isolation. Even a tiny air gap is a major problem...

Quote:
An alternate idea that we are discussing is building some some large dense panels that we can mount to the walls to cover the windows for the drum days - when the need to minimize the loudest noise is most critical.
Right. Technically that's called a "window plug", and it will work, with a few caveats.... Firstly, the exiting glass still needs to be good enough and well sealed enough that it can act as the outer leaf. Secondly, you need to figure out a way to be able to install and remove the plug easily while also attaining perfect seals around the edges. And thirdly, you have to have enough mass on the plug to provide the isolation that you need, when combined with the mass of the existing glass. So it can be done, but it has to be properly designed for the purpose (read: mathematics!) and built carefully.

Quote:
Another idea that I am curious about is glass blocks. Do they provide a lot more isolation?
Oh yes! Those would be a great alternative, provided that they are dense enough and very well sealed in place. You could replace the entire window like that: take out the existing window and frame, and build the blocks in there, to seal carefully.

However (there's always a "however" in acoustics, isn't there?). There's the issue that you'd be stuck with something called "mass law". When you only have one leaf in a wall, instead of two, then "mass law" is the set of equations in physics that governs how well that leaf will isolate. The basic equation is this:

TL(dB)= 20log(W) + 20log(f) -47.2

Where:
W is the weight density of the panel, and
f is the frequency you are interested in

There's briefer approximation, that goes like this:

TL = 20 log (F * M) - 47 dB (where F is the frequency (Hz), M is the mass per unit area (kg/m²) )

If you do the math with either of those, and plug in the frequencies typically found in drums and bass amps, plus the density of typical glass blocks and single leaf walls, you'll see that you don't get much isolation from Mass Law! You need a LOT of mass to get even reasonably decent isolation.

If you want an overall estimate of the isolation of the entire wall as a whole, not considering individual frequencies, then the empirical equation for that is:

TL = 14.5 log (Ms * 0.205) + 23 dB (where: Ms = Surface Mass in kg/m2 )

Once again, you'll see that you need large amounts of mass if you want to isolate to high levels: That's why studios are almost never built with single-leaf construction. They are done with two-leaf construction, which involves a different set of equations that are a lot more friendly! :)

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.


Report this post
Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 

All times are UTC + 10 hours


Who is online

Users browsing this forum: No registered users and 38 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group